Plural antenna assembly



May 6 1958 `F. x. BUCHER ETAL PLURAL ANTENNA ASSEMBLY Filed sept. 2.1953 Risparmi/a MA TCH/Nq asv/ce TRANSPO//DR D/SNC'E PLURAL ANTENNAASSEMBLY Francis X. Bucher and Richard J. Fahnestock, Nutley,

and Frank l. Lnndburg, East range, N. J., assignors .to InternationalTelephone and Telegraph Corporation, Nutley, N. J., a corporation ofMaryland Application September 2, 1953, Serial No. 377,995

12 Claims. (Cl. 343-726) No. 229,629, filed June 2, 1951, for Antennas,an antenna assembly is disclosed for use as an omnidirectional radiobeacon. This beacon antenna assembly comprises a cage structurecontaining a rotating dipole antenna and a loop antenna disposedsymmetrically with respect to the dipole to provide a rotating patternin the form of a cardioid which is generally horizontally polarized. Inthis beacon antenna assembly the cage structure is extended verticallyabove the portion containing the two antennas, this extension beingrequired to suppress the vertical polarization component rof the beaconradiation that would otherwise be present if it Were not for this upperextended section.

One of the objects of the present invention is to incorporate in theupper cage structure of this type of beacon antenna one or moreadditional antenna units without altering the beacon radiationcharacteristics thereof.

Another object is to provide a type of antenna within I havingindependent radiations, combined within a single j structure normallyrequired for one of said antennas thus economizing in supportingstructures and overall dimen- .sions otherwise required' by the threeunits when separated.

The above-mentioned and other objects of this invention will become moreapparent upon reference to the following description taken inconjunction with the accompanying drawings, wherein:

Fig. l is a view in side elevation of an omnidirectional radio beaconwith parts broken away illustrating the incorporation of two additionalantenna units therein in accordance with the principles of thisinvention; and

Figs. 2 and 3 are cross-sectional views taken along lines 2-2 and 3 3,respectively, of Fig. l.

Referring to the drawing, Fig. l shows an omnidirectional radio beaconprovided with a counter-poise 1 above which is disposed a smallrotatable dipole 2. The dipole is driven by a motor 3 which is supportedon a dielectric platform t. The dipole is rotated at 1800 R. P. M. toproduce a rotating ligure-of-eight radiation. Above the dipole is a loopantenna 5 adapted to produce a circular radiation. Surrounding theantennas 2 and 5 is a first or outer cylindrical cage 6 havingconductive pieces at the bottom and top thereof, such as indicated bythe top piece 7. The cylindrical wall of the cage comprises a pluralityof spaced conductive rods 8, as indicated more clearly in Figs. 2 and 3.This outer cage functions as a resonator energized by the antennas 2 and5. The spacing of the en-d pieces at 1 and 7 is preferably selectedslightly greater than a half wavelength of the lowest operatingfrequency. The rods 8 are spaced 2,834,013 Patented Mayv 6, 1 958 2sulliciently close together to provide anetfective vertical polarizationscreen or filter -sothat only horizontally polarizedenergy-passes. Eachtwo adjacent rods 8 -form effectively the boundaries of a shortsection'of waveguide which acts as the ultimate radiators. As it islonger than a half wavelength it will freely pass radiated energyin theTEN mode.

The structure so far described will provide-a rotating radiation fieldpattern in the shape -of a cardioid which will be generally horizontallypolarized. Howevendue to the resonator yaction of the cage ya certainamount-of vertical polarization may be radiated from the'cage `structuredue to radiation about -the upper end of the cage. This verticalpolarization is substantially entirely overcome by extending thecagestructurerone or moreflengths vupwardly above the cage whichcontains the two antennas 2 and 5. -This upper structure is indicated bythe -tw-o sections 9 and 10. From experience it is found that rthisupper structure should extend about yl2 feet above the cage section 6 inorder to satisfactorily suppress undesired vertical polarization. lSincethe 4dipole 2 is short with respect to the wavelength it would normallytend to have a low radiation resistance and an undesirable highcapacitive reactance. The resonator formed bythe cage 6 does not fullyIovercome this deliciency of the short dipole. In order to load thedipole antenna properly to achieve a desired compensation, the loopantenna 5 -is mounted and formed as apart ofa second or inner cage 6acomposed lof a plurality of circularly disposed vertical rods 8a. Whenthe loop antennais properly adjusted vertically within the cage, the`spacingthereof `with respect to the lower end of the cage will be lessthan a half wavelength in the uppermost frequency so thatthe resonatoraction of the cage will be inductive.

.In the operation of the beacon, two transmitter units.12 I

i6 and thence through transmission line 17 to the dipole 2, and theother through a phaser 18 -to a second relay 19 for application throughthe adjustable matching device 20 and transmission line 21 to the loopantenna 5. The rotating antenna 2 is driven by motor 3 from a powersource 22. The rotation of the dipole 2 producesv a reference signal bymeans of a tone-wheel 23 from the shaft of the motor 3. This referencesignal, which is applied to the transmitter 14 through connection 24 isfrequency modulated, for example, from about 9.48 to 10.44 kc. at a rateof 30 C. P. S. This reference signal modulates the V. H. F. signal tha'tfeeds the loop antenna. All modulation is removed from the portions ofthe V. H. F. signal that feeds the dipole. The rotation of thedipolealso produces a 30 C. P. S. variable phase signal which is in theform of a space modulation.

From the kforegoing description of the omnidirectional beacon it will beclear that an omnidirectional radiation pattern is obtained by means ofthe rotating dipoleZ,

the omnidirectional radio beacon, we also employ these cage sections foradditional functions. In section 9 we provide an antenna 25 for distancemeasuring equipment (D. M. E.). The D. M. E. antenna 25 preferablycornprises a vertical stacked array of antenna units 26a whereby avertical polarized omnidirectional radiation pattern is obtained, thearray insuring a flat substantially horizontal lobe. The antenna unitsmay be fed so as to tilt the radiation beam up or down with respect tothe horizontal plane as may be desired. Such an array suitable for thispurpose is disclosed in U. S. Patent 2,533,236. The cage section 9 issubdivided by a plate 27a thus dividing the section into two parts eachless than one-half wavelength long at the omnidirectional beaconfrequency to thereby render more uniform the wave front radiation of theD. M. E. antenna. While the antenna 25 does not atfect adversely theradiation pattern of the omnidirectional beacon, we find it necessary toincorporate a secon-d cage formed by an inner row of equally spacedconductive rods 26 circumferentially of the stacked array. The rods 26may be of the same diameter as the rods 8a of the first or lower section6. The two cages thus provided about the D. M. E. -antenna act as ifthey were a double-stub tuner and thereby serve to match the D. M. E.antenna to the free space about the outer cage. In other words, the D.M. E. antenna is a source of S-band energy which propagates through theopenings between the adjacent rods of each of the concentric cages, therods being spaced with openings equal to or greater than a halfwavelength at the frequency of the energy propagated by this antenna.The openings or spaces between the adjacent rods of the cages imposedis' continuities to the radial propagated wave. The radius of the innerrow of rods 26 is chosen so as to place the proper discontinuity in sucha position that it will serve to match along with the discontinuityimposed by the outer row of rods 8a the wave impedance of the source tofree space. This is similar in effect to the operation of a fixeddouble-stub tuner on a two-wire transmission line.

By locating the D. M. E. antenna 25 within the double cage section 9 theonly influence of the cages observed is the suppression of minor lobesof the D. M. E. antenna. This tendency to suppress the minor lobes,however, operates to Yconcentrate more energy into the major lobes whichresults in increasing the effective range of the D. M. E. antenna. TheD. M. E. radiation pattern is vertically polarized and has no adverseeffect upon the radiation of the omnidirectional beacon of section 5.

The feed line cable for the antenna 25 preferably passes through one ofthe rods of the outer or inner cages of section 6. As shown it isextended up through a hollow rod 27 to the input connector 28 of theantenna 25.

in the top-most section l!) we provide microwave beacon antenna 29 whichmay be of the type disclosed in the Massachusetts Institute ofTechnology, Radiation Laboratory Series. volume l2, pages 325 to 328.The beacon antenna 29 is divided into a receiver section 30 and atransmitter section 31. By disposing these two sections on a commonvertical axis the radiation pattern of each is substantially independentof the other. The radiation patterns of the beacon antenna sections arenot affected by the conductors 8 since at the microwave frequencies useda half wavelength is very much shorter than the spacing between theconductors 8 and also than the distance between the upper and lowerplates of the cage section 10. The waveguide feed lines for the twoantenna sections Sti, 3l must be brought up along the cage withoutaffecting the radiation patterns of the lower antennas. This is done byenlarging two fof the cage conductors in the form of rectangularwaveguides as shown at 32 and 33. The waveguide 32 is coupled to thetransmitter section 3l while the waveguide 33 is coupled to thereceiving section 30. The lower end of the waveguide 32 is likewisecoupled to a transponder E24 while the lower end of the waveguide 33* iscoupled to a responder 35, the transponder and the responder unitsprovided for two-way communication.

The reason why the cage structure in the upper two sections suppressessome signals while passing others is apparent from the Well-known theoryof structures such as waveguides and of slots in conductors.Electromagnetic waves lare propagated through such a structure if thedimension perpendicular to the direction of polariza` tion of theelectrical field is a half wavelength or greater, and are suppressed ifthe dimension is less than a half wavelength. Thus, each dimensionestablishes a cutoi frequency for modes in which the electric field isperpendicular thereto. In cage section 9, the spacing of the rods issuch that for vertically polarized signals the cutoff frequency isbetween the frequency of the omnidirectional antenna and the frequencyof the D. M. E. antenna. ln the `cage section 1d, the frequencies of themicrowave beacon are very high, and therefore the wavelengths are veryshort compared to all dimensions of the openings in the cage.

From the foregoing it will be clear that the three antenna sections ofthe assembly shown in Fig. l operate independently and without anyadverse interference with the others. The omnidirectional antenna systemof the lower section 6 requires the upper sections 9 and 10 of the cagestructure to suppress the vertical polarized component of its radiatedenergy. The D. M. E. antenna of section 9 employs the outer cage 8 forits feed line leads and, in conjunction with the inner cage formed byconductors 26, as a tuned filter for the passage of vertically polarizedradiation properly matched to the open space about the outer cage. Whilethe D. M. E. antenna does not affect the operation of the cage as asuppressor of the vertical polarized `component of the omnidirectionalantenna means of section 6, the cage structure thereabout enhances theradiation pattern of the D. M. E. antenna by increasing the range of themajor lobes thereof. The beacon antenna of section 10 also employscertain of the conductors of the outer cage as leads for coupling thetransmitter and receiver sections thereof to the corresponding groundequipment. The surrounding cage does not affect adversely the radiationpatterns of section 3()V ably less than where such antennas are mountedinde.

pendently of each other.

While we have disclosed the principles of our invention in connectionwith specilic apparatus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation tothe scope of our invention, as set forth in the objects thereof and inthe accompanying claims.

We claim:

l. ln combination. an omnidirectional antenna assembly cornnrising avertically disposed cylindrical cage structure divided by a conductiveplate into lower and upper antenna sections, iirst antenna meansdisposed in the lower section to produce a radiation patternhorizontally polarized at a first frequency, second antenna meansdisposed in said upper section to produce a radiation pattern verticallypolarized at a second frequency, the upper cage section being formed ofa plurality of circumferentially spaced vertically disposed conductorswith openings between them having a width of less than a half wavelengthat said iirst frequency and at least a half wavelength at said secondfrequency to suppress the vertical polarized component of the radiationfrom said lower section and to pass therebetween vertically polarizedradiation from said second antenna means.

2. The combination according to claim l, wherein the second antennameans comprises a stacked array of antenna elements and a second seriesof circularly spaced vertically disposed conductors with openingsbetween them at least a half wavelength wide at said second frequencylocated concentrically about said second antenna means within said cagestructure and constituting therewith a double tuned structure forimpedance matching between the radiators of said array and free space.

3. In combination, an omnidirectional antenna assembly comprising avertically disposed cylindrical cage structure divided by a conductiveplate into lower and upper antenna sections, first antenna meansdisposed in the lower section to produce a radiation patternhorizontally polarized at a first frequency, second antenna meanscomprising a beacon antenna system including a transmitter section and areceiver section disposed along a vertical axis coaxially of said cagestructure disposed within said upper section for radiation and receptionof signals in a second frequency range, the upper cage section beingformed of a plurality of circumferentially spaced vertically disposedconductors with openings between them having a width of less than a halfwavelength at said first frequency to suppress the vertical polarizedcomponent of the radiation from said lower section, the dimensions ofsaid openings being greater than a half wavelength in said secondfrequency range to pass therebetween radiation from said second antennameans.

4. The combination according to claim 3, wherein certain of the verticalconductors of said cage structure are in the form of waveguides, one ofsaid waveguide conductors being coupled to the receiver section and theother waveguide conductor being coupled to the transmitter section ofsaid beacon antenna.

5. In combination, a cylindrical cage structure, conductive platesdividing said cylindrical structure into three sections, the cylinder ofsaid cage being formed by a plurality of circumferentially spacedvertically disposed conductors, first antenna means disposed in thelower section of said cage structure for radiation of horizontallypolarized signals at a first frequency, second antenna means disposed inthe intermediate section for radiation of vertically polarized signalsat a second frequency, and third antenna means disposed within theuppermost cage section for radiation and reception of signals in a thirdfrequency range, the vertical conductors of the other two sectionsdisposed above said lowersection being spaced with openings of less thana half wavelength at said first frequency and at least a half wavelengthat said second and third frequencies to suppress any verticallypolarized energy of said first antenna means and to pass therebetweenthe energy of said second and third antenna means.

6. The combination according to claim 5, wherein said first antennameans comprises a rotating dipole and a loop antenna for radiation of acardioid pattern.

7. The combination according to claim 5, wherein the second antennameans comprises a vertically stacked array of antenna units forradiation of an omnidirectional pattern; and said intermediate cagesection includes an inner cage comprising a plurality ofcircumferentially spaced vertically disposed conductors with openings atleast a half wavelength wide at said second frequency which cooperatewith the vertical conductors of said intermediate cage section toprovide a double tuned structure for impedance matching of the radiatedenergy of said second antenna means with respect to free space.

8. The combination according to claim 5, wherein the third antenna meanscomprises a transmitting antenna section and a receiving antenna sectiondisposed axially of said cage structure; and certain of the verticalconductors of said cage are in the form of waveguides with meanscoupling one of said waveguide conductors to said transmitter sectionand means coupling the other of said waveguide conductors to saidreceiver section.

9. The combination according to claim 5, wherein said first antennameans comprises a rotating dipole and a loop antenna for radiation of acardioid pattern; the second antenna means comprises a vertical stackedarray of antenna units for radiation of an omnidirectional pattern; andsaid intermediate cage section includes an inner cage comprising aplurality of circumferentially spaced vertically disposed conductorswith openings at least a half wavelength wide at said second frequencywhich cooperate with the vertical conductors of the cage section toprovide a double tuned structure for impedance matching of the radiatedenergy of said second antenna means with respect to free space.

l0. The combination according to claim 5, wherein said first antennameans comprises a rotating dipole and a loop antenna for radiation of acardioid pattern; the third antenna means comprises -a transmittingantenna section and a receiving antenna section disposed axially of saidcage structure; and certain of the vertical conductors of said cage arein the form of waveguides with means coupling one of said waveguideconductors to said transmitter section and means coupling the other ofsaid waveguide conductors to said receiver section.

1l. The combination according to claim 5, wherein said first antennameans comprises a rotating dipole and a loop antenna for radiation of acardioid pattern; the second antenna means comprises a verticallystacked array of antenna units for radiation of an omnidirectionalpattern; said intermediate cage section includes an inner cagecomprising a plurality of circumferentially spaced vertically disposedconductors with openings at least a half wavelength wide at said secondfrequency which cooperate with the vertical conductors of the cagesection to provide a double tuned structure for impedance matching ofthe radiated energy of said second antenna means with respect to freespace; the third antenna means comprises a transmitting antenna sectionand a receiving antenna section disposed axially of said cage structure;and certain of the vertical conductors of said cage are in the form ofwaveguides with means coupling one of said waveguide conductors to saidtransmitter section and means coupling the other of said waveguideconductors to said receiver section.

l2. In combination, an omnidirectional antenna assembly comprising avertically disposed cylindrical cage structure divided by a conductiveplate into lower and upper antenna sections, first antenna meansdisposed in the lower section to produce a radiation patternhorizontally polarized at a first frequency, the upper cage sectionbeing formed of a plurality of eircumferentially spaced verticallydisposed conductors with openings between them having a width of lessthan a half wavelength at said first frequency and at least a halfwavelength at said second frequency to suppress the vertical polarizedcomponent of the radiation from said lower section and second antennameans disposed in said upper section to produce a radiation patternvertically polarized at a second frequency, the vertical slots formed bythe vertical conductors of said cage structure being at least a halfwavelength wide at said second frequency to pass vertically polarizedradiation from said second antenna means, said second antenna meanscomprises a stacked array of antenna elements and a second series ofcircularly spaced vertically disposed conductors with openings betweenthem at least a half wavelength wide at said second frequency locatedconcentrically about said second antenna means within said cagestructure and constituting therewith a double tuned structure forimpedance matching between the radiators of said array and free space,one of the vertical conductors of said cage structure being hollow and afeed line is contained therein for coupling to said antenna array.

References Cited in the file of this patent UNITED STATES PATENTS2,533,236 Felsenheld Dec. l2, 1950 2,640,930 Lundburg et al June 2, 19532,726,388 Kandoian Dec. 6, 1955

